Engine rattle under acceleration

Discussion in 'Small Block Tech' started by JN_Skylark, Dec 25, 2020.

  1. Quick Buick

    Quick Buick Arlington Wa

  2. JN_Skylark

    JN_Skylark Well-Known Member

    Looks like some research is in order, maybe Larry can chime in
     
  3. Quick Buick

    Quick Buick Arlington Wa

    FWIW Im on the same boat as you... New motor last October. trying to get it dialed in.. chasing the same tings as you... Got her down to no tinging with no vac... Its all play it by the rain..
     
  4. JN_Skylark

    JN_Skylark Well-Known Member

    It's frustrating but it's part of the learning experience, fortunately these cars are easy to tinker with :) It is interesting to see how a small change can have a noticable effect
     
  5. JN_Skylark

    JN_Skylark Well-Known Member

    Looking through my manual it looks like the gap should be 0.030" instead of the 0.035" I believe I have it set to. So my short list of things to check is:
    1) Confirm/record WOT run on level ground and uphill, pinpoint when detonation/pinging occurs (although I don't have a tach)
    2) Confirm initial/total timing. My last adjustment was 10* initial 25* total
    3) Check gap on plugs

    Any other suggestions?
     
  6. Quick Buick

    Quick Buick Arlington Wa

    The weather is a big noticeable affect... Finding that sweet spot between the fronts this time of year is a pain.
     
    JN_Skylark likes this.
  7. JN_Skylark

    JN_Skylark Well-Known Member

    Agreed
     
  8. Quick Buick

    Quick Buick Arlington Wa

  9. Quick Buick

    Quick Buick Arlington Wa

  10. Quick Buick

    Quick Buick Arlington Wa

  11. JN_Skylark

    JN_Skylark Well-Known Member

    I do have a dwell meter, it's an old school one that works pretty good. Last time I adjusted the points with the meter it was 30*, 25* was referring to my total timing.
     
  12. JN_Skylark

    JN_Skylark Well-Known Member

    I was planning on taking a clip of the car at wide-open tonight on my way home, but weather intervened and it didn't seem wise to drive wide open with one hand on wet roads. I did make two short clips of the distributor advance, I found my distributor shaft has up/down movement which doesn't seem right to me. Hopefully one of you guys can school me

    Clip #1

    Clip #2
     
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    UR-4 approximates an AC R45TS

    UR-5 approximates an AC R43TS
     
  14. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    It's pretty common for there to be some up and down movement. If it is excessive, you'll see the timing mark jump around and not be steady. .012-.020 is generally OK. They sell shims to take up excessive slack. It is more important that there be no side to side shaft movement. That would cause a big dwell variation, and that directly affects ignition timing.
     
    72gs4spd likes this.
  15. 72STAGE1

    72STAGE1 STAGE 1 & 2

    It’s been my experience over the years that numbers are just baseline and each engine is different. Having said that, where’s the flaw with doing this old school?As in once the plugs are right, carb is right, dwell is right, then there’s the timing....I have always been a believer of advancing till she “pings” then back it off until it doesn’t... That’s my optimum timing no matter what the number either 32deg. or 35 deg. it’s really irrelevant. Doesn’t matter if it’s my Camaro, Mustang, or my GS. That’s where they run their best.

    All these numbers sometimes just get in the way, heck don’t even need a timing light.

    Am I missing something?
     
    Last edited: Feb 28, 2021
  16. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yeah, sure, you could do it that way, but it's inherently imprecise. Since the distributor turns at half crank speed, 1* of distributor rotation equals 2* at the crank. Advancing it till it talks to you, then backing it off makes sense in the absence of a light, but if you really want to dial it in, the best method is to know precisely what the timing is, so you have a baseline for change. Moving the distributor without that knowledge almost guaranties that you'll move it too much one way or the other. It helps to have a chassis dyno or be at the track. Optimal timing will produce the best rear wheel HP or trap speed. Then a light tells you exactly where you are, and what produced the best results.
     
  17. 72STAGE1

    72STAGE1 STAGE 1 & 2

    Yes Sir, using the light is to CONFIRM where your timing is at, my method can get you there in the first place, and then the light can get you there again. Learning to move the distributor in small increments is key yes 100% agree.

    Thanks for your input Larry
     
    Last edited: Feb 28, 2021
  18. Quick Buick

    Quick Buick Arlington Wa

    Are you really running Arco..... I can tell a ARCO burner form a 76er without even talking to the person driving..... When the car is fully warned up to operating temp. A ARCO car drips more water out the exhaust than a 76... a 76 car will drip more water than a Corn free car.... Costco Safeway Albertsons are all piss gas. I've had much better luck with 76 in this area.... FWIW 4 mpg difference in chevron VS 76.. in both a 96 subaru outback and a 92 5.0 Caprice..
     
  19. Jim Nichols

    Jim Nichols Well-Known Member

    Another Washington resident. I only use Chevron and Shell gas.
     
  20. JN_Skylark

    JN_Skylark Well-Known Member

    Would stock gap be recommended or is gap something that can/should be experimented with?

    Fortunately in my case side to side movement is solid, but up and down movement seems more than 0.012-0.020 like you mentioned according to my eyeball (take with a grain of salt). Where can I find these shims?
     

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